The present invention relates to subterranean operations involving deviated well bores, and more particularly, to methods of maintaining the structural integrity and conductivity of deviated well bores.
A deviated well bore, as that term is used herein, refers to a well bore that is not substantially vertical. The term “deviated well bore,” as the term is used herein, also includes horizontal well bores. Deviated well bores are becoming more prevalent, because in part, they allow one rig and well head to drill and produce from a much larger reservoir area than a more traditional vertical well bore. Thus, deviated well bores are often an attractive option for producing desirable fluids from subterranean formations such as, for example, hydrocarbons from oil and gas reservoirs.
Although deviated well bores provide a variety of advantages, unfortunately, they can also present some serious drawbacks. One drawback of deviated well bores is that they can be prone, in some cases, to structural weaknesses relative to vertical well bores. Moreover, inserting and placing well bore casing in deviated well bores to counteract these potential weaknesses is often impractical and technically complex. Further, placing casing in a deviated well bore can be prohibitively expensive. As a result, many deviated well bores are simply left as open holes without any casing that might provide structural support, which may allow the deviated well bore to fail or collapse, which is undesirable. Well bore structural failures are extremely disadvantageous, because such failures can negatively affect the conductivity of the well bore among other problems. In some cases, a failure or collapse of a deviated well bore can result in a total production blockage of hydrocarbons or other desirable fluids from the well bore. Solely for illustrative purposes, FIG. 1 shows an example of a failed deviated well bore 110 with a partial open hole collapse 120 obstructing the production of hydrocarbons from the surrounding subterranean formation 130.
An example of one type of deviated well bore that is particularly prone to collapse is one penetrating a coal bed formation. Coal bed formations are particularly friable and fractured and, as such, are prone to collapse. Moreover, inserting casing in a coal bed formation to counteract the propensity for well bore collapse can potentially lead to an undesirable explosion because of the frequent presence of methane therein.
Another example of a deviated well bore that is particularly prone to structural failure is one that has been subjected to previous stimulation operations. Stimulation or fracturing operations can disturb a formation in such a way as to induce shifts or perturbations in the formation, thus leading to a greater risk of a structural failure of any type of deviated well bore drilled therein.